Continuous process of producing esters from aqueous solutions of aliphatic acids



Patented Aug. 27, 1935 UNITED STATE CONTINUOUS rnoocss F. rnonucnvof ESTERS FROM AQUEOUS SOLUTIONS OF I ALIPHATIC ACKDS Henri Martin Guinot, Melle, France, assignor to i Commercial Solvents Corporation, N. Y., a company of Maryland New York,

No Drawing. Application May 15,,1931,;. Serial No. 537,749. In France May 16, 1930 3 Claims. (Cl. 260- -106) As a rule esters are obtained by causing an alcoholto act, in a continuous or discontinuous way, upon an acid. It'is known that, in order to 1 obtain a substantially" quantitative esterification 5 process, it is necessary to continuously eliminate cause they can be applied only to the production of esters from alcohols and acids capable of esterifying very quickly, suchfor instance as I methyl formates and acetatesand ethyl f ormates and acetates (see for (instance German Patent 354,863 andFrenchf Patent 544,288) Furthermore, these methodshave the disadvantage that they necessitate the use of large quantities of "a catalytic mineral acid anddo not ensure com plete extraction-of the'acid from the solutions that are utilized.

My invention makes it possible to utilize dilute aqueous solutions of fatty acids for the obtainmentiof all the aliphatic esters, whatever they maybe: My invention is characterizedby the combination of twooperations, the first of which iswell known per se.;

1. Extraction of the dilute acid bymeans of a; solvent or of a mixture of suitably chosen solvents, and byany method whatever among those alreadyknown;

. '2'. Direct treatment of the acid-solvent mixture thusqobtained, which v mixture always contains still a 'smallyamount of water,; so as to esterify the acid contained therein.

This esterification canbe performed according to'the principles of the methods already known. However, it may more advantageously be efiected' in accordance with the examples which will be hereinafter described, and which form a part of my invention; f e The solvents that can .be utilized must meet the following requirements: 1(a); They must be insoluble or very little soluble in water;

.(17) They must have a good capacity of extracting the acid; (0) @They must not prevent the separation of i hat they i s he ebe corresponding ester. k j v Itshould be noted thatGoering (German? ,t-

the products that will formed: during the subsequent esterification';

(d) They must not form w th the aeidin the heated state any decomposition product which.

might deteriorate'the apparatus or-contam inate theesterformed.

I have found that. these conditions]? ere,

filled in. a perfect manner when utilizin' as a solvent, either the .alcohol that is to be? est'erij fled, which, owing to its chemical affinity gor, the

acid, has a particularly favorable capacityoffer:

tracti0n,or the ester that it is desired rectum. Or else a mixture of the alcohol and-of the ester,

However my invention is .not limited to the use of these bodies. 'I may alsouse anotherester,

either alone or mixedwithanother body, :or-else bodies having any chemical function whatever, such. as hydrocarbons, ketones, and so 0:13pm:

' .mentionedire'g' quirements. v

For carrying out my process, three cases are to be considered, j g I First case'.-"'Ihe, ester to be obtained corresponds to an alcohol that is insoluble on is little v l y at r-s m1; in .th t case, it. is advantageous: to use .as' a solvent for the acid, the alcohol that is t0 esterif ed, the power 10f extraction of said. alcohol beingalwaysvery much higher, than ent--No.- 28,064 filed DecQlB, i883) hasbited alcohol as'one of thesolventscapableof being used for concentrating acetic acid. as a mat- I ter of fact, that method isnota'pplicablejbe: cause, during the distillation to which is sub-'- jected the extract in order to separate acid and alcohol..,from each other, theretakes place a partialest'erification which is contrary to the purpose of the. method, said purpose beinglto produce concentrated acid and not ester.

In the present *nvention, on the contrary, .it will not be endeavored to separate the acid-from thealcohol, but the mixture will be directly esteri- The dilutefacidsolution isffirst subjectedto a methodic, exhausting processgby" means of alcohol,..in the heated or in 'the cold; state, in any tion water.

' an az isolate the ester "in a pure state. The alcohol that is spent is continuously replaced by an equiv alent amount of fresh product, which isreturned with the alcohol that is not transformed, so as to indefinitely be used again for the extraction.

Example 1.-Production of butyl acetatejrom a 10% acetic acid solution volumes of a diluted acetic solution are subjected to a methodic exhausting, for instance in a series of apparatus working in a continuous manner, with 150 volumes of butyl alcohol. Owing to the high coeflicient of extraction of butyl alcohol with respect to acetic acid, (1 to 1.2 complete exhaustion of the solutions is easily obtaine'd. The extract issuing from theapparatus contains 6.7% ofacid and a small amount of water which iseasily v eliminated during the subsequent distillation together with the esterificahe' solution.lof aci d in alcohol ,is introduced into afplatecolunm in which the acid is com pletely and quickly 'esterified owing to the prose ence. ot a large excess of alcohol, and to the im-' mediate and continuouselimination of water ei ther in the form'fof a ternary azeotropic mixture boiling at 89.5? (23.7% of water) or in the form of an" lcohol 'water binary mixture boiling at Q2f{'(35% ofwater). Y Q'Ih'ef ester is separated in the pure state, by a known method, from the alcoholin excess, which iis returned indefinitely to the extraction apparatus. "It sufiices to replace the alcohol that is spent byfresh alcohol.

Ewample 2. Preparation of hutyl lactate from an 8% lactic acid solution.- I r 'make' use of butyl alcohol as a's'olvent in the ratio of ZQO volumes of butyl alcohol for 100 volumesof diluted" acid The extract contains about. 4%fof lactic acid- It is treated in exactlyj thesame manner as described concerning Example 1. Owing to the considerable diiference between the boiling points of butyl alcohol and butyl lactate (190-7200 the separationcan'be efiectedwithout, diificulty, the lactateiremaining'as 'a'residue.

'jfSecond case. e ester corresponds to anal: cohol' soluble in water. t j

In thaty case, the extraction pf the acid by thalcohol being not possible, I utilize as a solvent the estertobe obtained. ,Saidester always ha 'fijboilingqpoint lower .thanthat'o fth e acid 1 tobeextracted, so that, during .theseparation'of the ester from. the acid: obtained by' distillation on the plates ofacolumn alcohol is fed in a continuous manner, andbeing in presenceof an excess of acid, said alcohol esterifies rapidly., It suificesto removefrom the circuit in a continu "ous manner the quantity of ester corresponding :to' the acid extracted. 'As for thesmall amount of waterintroduced by. the feed mixture, it is driven or: dur ng the. distillation i the form f h j tropicjmixture simultaneously with the esterification'water itselt,f p i v p t lt'rample' 3-. Preparat ion. of ethyl acetate from face'tic' solutions at 15% 0btained during the manufacture ofpcellalose acetate.

" The diluted acetic solution is methodically exfresh material only to replace mechanical losses or evaporation losses.

- hausted in a continuous manner by means of a volume of ethyl acetate which is equal to twice that of the solution. The extract leaving the apparatus contains 7.5% of acetic acid. That mixture is introduced in a continuous manner into a plate column into which is introduced ethyl alcohol. The presence of an excess of acid with respect to the amount of alcohol that is added and the continuous elimination of water by ethyl acetate in the format an azeotropic mixture boiling at 70.45", and containing 8.2% of water producea rapid esterification of the alcohol. The ester is easily separated. I remove continuously in the pure state the amount of ethyl acetate that correspondsto the acid contained in the extract, that is about 11 kilograms for 100 kilograms of extract submitted toth'e esterification process.

The remaining ester, corresponding to the amount originally used for the extraction, is utilized for the succeeding extraction. In this manner the original amountof ester is continuously recycled in the-process, it being necessary to add Example 4.-Productzon of ethyl butyrate The starting solution is an aqueous solution of butyric acid at 18%, corresponding to a mixture havinga minimum boiling point. As ethyl alcohol is soluble, the extraction ,of butyric acid is obtained by means of, ethyl butyrateitself (0.5 vol.). The extract issuing from the apparatus, which contains 36% of butyric acid, is

treated in a column into which is introduced in a continuous manner ethyl alcohol. ,Theopera tion is quite analogous to that described in Example 3. is obtained in a very pure state.

Third case. It may happen that theester to be prepared is itself soluble in the acid solution to be extracted. In that case, I add to said ester, in order to effect extraction, another esterv ora supplementary solvent insoluble or little soluble in water, and chosen in such manner that it may subsequently be easily separated from either the ester obtained, or the acid itself.

Example 5 In order to prepare methyl acetate (boiling point 57) I may use as a supplementary solvent isopropyl acetate the boiling point of which (88) allows an easy separation from acetic acid- (boil ing point 118) and methyl acetate. 3 1

Theisopropyl acetate will'also serve to entrain water during the distillation. For it 'formswith water a mixture having a minimum boiling point which boils at 60 andcontains 10% of water.

In order'to carry out the process according'to my' invention Imay use any of the known extracting apparatus operating eitherin the cold or in the hot state (column with'a' filling'ma terial, battery of apparatus withdecanters)", I

Finally I may point out an interesting appli: cation of the present invention, when it is desired to perform esterification as an accessory operation in the general manufacture of a'concentrated acetic acid. 7 I V I There are industrial plants for concentrating fatty acids by a method employing esters as solvents oras entraining bodies. the case of the concentration of' vinegar for obtaining anhydrous acetic acid which is to be used for the manufacture of cellulose acetate artificial silk. It may be interesting to add to The ethyl butyratawhich boils at 120,

It is forinstance this process of manufacture a supplementary production of esters. By applying the principle of the present invention I make it possible to avoid the necessity of a special apparatus for esterification. I introduce into the closed circuit in which the solvent or the entraining body flows, in a continuous or in a discontinuous manner, a certain quantity of alcohol corresponding to the amount of ester to be produced. The esterification process will take place by itself in the part of the apparatus in which the acid is separated by distillation from the solvent or from the entraining body. It will suffice to remove the ester that will be formed at a point of the circuit suitably chosen according to the methods that are used.

It will be possible, without departing from the principle of my invention to use any of the known esterification processes or to make some modifications of detail in the process above described, for instance to work, wholly or partly, at a pressure different from atmospheric pressure, provided that said modifications come within the scope of the appended claims.

What I claim is: 7

l. A method of producing esters from diluted aqueous solutions of aliphatic monocarboxylic acids which comprises the step of first extracting the acid from its solution by means of a substantially water immiscible solvent selected from the group consisting of an aliphatic primary monohydric alcohol that is to be esterified by said acid and an ester that is to be produced from said acid, removing the aqueous residue and thereafter directly fractionally distilling said extract in the presence of such alcohol to directly esterify the acid contained in the said extract, removing the water of reaction whereby the distilling mixture is maintained in a substantially anhydrous state'and finally separating the resulting ester'irom the distillation residue.

2. A method of producing esters from dilute aqueous solutions of aliphatic monocarboxylic acids which comprises the step of first extracting the acid from its solution by means of a substantially water-immiscible aliphatic primary monoseparating the resulting extract from the aqueous residue and thereafter directly fractionally distilling said extract while maintaining the concentration of alcohol in excess ofthe concentration.

of acid in said extract, and removing the water of reaction whereby the mixture ismaintained in a substantially anhydrous state, thereby directly esterifying the acid contained in said extract.

3. A method of producing esters from dilute aqueous solutions of aliphatic monocarboxylic hydric alcohol that is to be esterified by said acid,

acids which comprises the step of first extracting the acid from its solution by means of a substantially water-immiscible aliphatic alcohol ester that is to be produced from said acid, separating the resulting extract from the aqueous residue and thereafter directly fractionally distilling said extract in theprese'nce of the alcohol to be 

